Fix unw_getcontext() return value on AArch64.

unw_getcontext() should return UNW_ESUCCESS on success.  Therefore, the
assembly for AArch64 is incorrect because "ldr x0, #0" is a PC-relative
load instead of an immediate value load.

llvm-svn: 240648

libunwind/src/UnwindRegistersSave.S

@@ -277,7 +277,7 @@ DEFINE_LIBUNWIND_FUNCTION(unw_getcontext)
   stp    d28,d29, [x0, #0x1F0]
   str    d30,     [x0, #0x200]
   str    d31,     [x0, #0x208]
-  ldr    x0, #0                   // return UNW_ESUCCESS
+  mov    x0, #0                   // return UNW_ESUCCESS
   ret
 
 #elif defined(__arm__) && !defined(__APPLE__)

libunwind/test/unw_getcontext.pass.cpp

@@ -0,0 +1,8 @@
+#include <assert.h>
+#include <libunwind.h>
+
+int main() {
+  unw_context_t context;
+  int ret = unw_getcontext(&context);
+  assert(ret == UNW_ESUCCESS);
+}